Field of the Invention
The present invention relates to a gas compressor of an air conditioning unit mounted in a vehicle, for example.
Description of the Related Art
A vehicle such as an automobile incorporates an air conditioning unit for controlling the temperature of a vehicle interior, for example. Such an air conditioning unit has a loop-like refrigerating cycle in which refrigerant as a cooling medium is circulated. The refrigerating cycle is comprised of an evaporator, a gas compressor, a condenser, and an expansion valve in order. A gas compressor is provided in the air conditioning unit to generate high-pressure refrigerant gas by compressing gaseous refrigerant evaporated through the evaporator and transmit it to the condenser.
In related art a vane type rotary gas compressor is known, which comprises a cylinder having an elliptical inner circumference in which a rotor with vanes is rotatably supported. The ends of the vanes are slidable on the inner circumference of the cylinder and the vanes are allowed to slide into and out of the rotor.
This vane type rotary gas compressor comprises a compressor body including a rotor rotatable integrally with a rotational shaft, a cylinder surrounding the outer circumference of the rotor, vanes allowed to slide from the outer circumference of the rotor to the inner circumference of the cylinder, and two side blocks sealing the respective ends of the rotor and cylinder and rotatably supporting both ends of the rotational shaft.
In the compressor body, two adjacent vanes in a rotor's rotational direction work to decrease the volume of compression chambers formed between the rotor outer circumference and cylinder inner circumference along with the rotation of the rotor. Thereby, low-pressure refrigerant gas in the compression chambers is compressed into high-pressure refrigerant gas and discharged to a discharge chamber. The high-pressure refrigerant gas is discharged outside from the discharge chamber after oil components such as refrigerant oil are separated. The separated oil is accumulated at the bottom of the discharge chamber.
The oil accumulated in the discharge chamber is pressed by the high-pressure refrigerant gas and supplied to vane grooves through the two side blocks and oil paths and chamfered grooves of the cylinder inside the side blocks, and it works as back pressure to protrude the ends of the vanes from the vane grooves. The oil supplied to the vane grooves is at intermediate pressure lower than the high-pressure ambience of the discharge chamber due to a pressure loss since it has passed through a small gap between a shaft bearing and the outer circumference of the rotational shaft.
However, in the last stage of compression process the pressure in the compression chambers goes higher than the intermediate pressure and this high pressure acts on the ends of the protruding vanes. If the back pressure onto the vanes remains at the intermediate pressure, the pressure in the compression chambers exceeds the intermediate back pressure and a centrifugal force from the vanes' rotation. This may cause chattering, that is, a phenomenon that the vanes' ends repeatedly collide with and separate away from the inner circumference of the cylinder.
In view of this, Japanese Laid-open Patent Application Publication No. 2002-327692 discloses a gas compressor in which oil at a higher pressure than the intermediate pressure is supplied through a high-pressure supply hole to the vane grooves when the inner pressure of the compression chambers is heightened in the last stage of the compression process.
In this gas compressor the high-pressure supply hole is formed in one of the side blocks to supply the oil accumulated at the bottom of the discharge chamber to the vane grooves by the pressure of the refrigerant gas discharged to the chamber. This can prevents chattering.
However, if an unnecessarily large amount of oil is supplied to the vane grooves through the high-pressure supply hole, the necessary oil amount accumulated in the discharge chamber is increased. The amount of oil contained in the gas compressor is increased accordingly, increasing the weight and costs of the compressor. Therefore, the diameter of the high-pressure supply hole needs to be formed small enough to prevent an excessive supply of oil.
However, the side blocks are made from aluminum alloy or the like, and forming a small diameter hole in a certain position of the side blocks by deep hole processing requires high processing technique, resulting in low workability and increased manufacturing costs.